The relative merits of open‐ and closed‐path analysers for measurement of eddy fluxes

摘要: Theoretical and practical aspects of measuring eddy fluxes trace gases using open-and closed-path analysers are presented. Trace gas measured with an open-path analyser require the concurrent measurement sensible latent heat to correct for density fluctuations in concentration caused by these fluxes. A eliminates corrections due flux, but not water vapour, provided temperature completely removed without significantly reducing mixing ratio. Theory design exchangers attenuation during air flow through tubes is used provide criteria systems. Spectral transfer functions estimate flux losses sampling tube analyser. Other factors considered include cross-sensitivity infrared CO2 deterioration system performance contaminants on walls tubes. Of two open-path, tested, one showed a strong interaction between while other little sensitivity presence than dilution. commercial also vapour. Compared results clean tube, spectral bandwidth vapour decreased after several weeks sampling. No such was observed CO2. These findings attributed differential adsorption/desorption dust or salt tubing walls. Rain must be from obtain satisfactory measurements. Careful maintenance required both open- systems ensure long-term With precautions, approaches will